Generally, polycarbonate/styrene containing copolymer blends are resin mixtures which have good processability and high impact strength. Therefore, polycarbonate/styrene containing copolymer blends have been widely used in large injection molded products, such as computer housings or other office supplies, which emit a lot of heat. Accordingly, flame retardancy, heat resistance and high mechanical strength are important factors that should be considered when manufacturing the blend.
Halogen-containing flame retardants and antimony compounds are conventionally used to impart flame retardancy to the resin composition. However, when a halogen-containing flame retardant is used, it can produce very toxic gases during combustion. Therefore, the demand for the resin without halogen flame retardants is increasing. One well known and widely used method for imparting flame retardancy without using halogen-containing flame retardants is to use a phosphate ester flame retardant.
U.S. Pat. No. 4,692,488 discloses thermoplastic resin compositions containing a non-halogen aromatic polycarbonate resin, a non-halogen styrene-acrylonitrile copolymer, a non-halogen phosphorous compound, tetrafluoroethylene polymer, and a small amount of ABS copolymer.
U.S. Pat. No. 5,061,745 discloses a flame retardant resin composition containing an aromatic polycarbonate resin, an ABS graft copolymer, a copolymer and a monomeric phosphate ester.
However, the resin compositions described above have a disadvantage in that it is necessary to add an excessive amount of phosphate ester flame retardant in order to obtain a certain level of flame retardancy.
A large amount of flame retardant also needs to be added to impart flame retardancy to blends of polycarbonate resin and polymethyl methacrylate resin, due to the lack of flame retardancy of polymethylmethacrylate resin. The amount of polymethylmethacrylate resin may be decreased to try to improve flame retardancy, but reducing the amount of polymethylmethacrylate resin may also decrease scratch resistance.
U.S. Pat. No. 5,292,786 discloses a composition having good weld line strength by using a phosphoric ester compound as a flame retardant and by further adding a polymethylmethacrylate resin to a polycarbonate resin and a styrenic resin. However, it is difficult to obtain improved scratch resistance and flame retardancy, since the amount of a polymethylmethacrylate resin which contributes to the property of scratch resistance is relatively small, in addition to the fact that polycarbonate resin and styrenic resin do not have good scratch resistance.
Japanese Patent Laid-Open No. 1999-199721 discloses a flame retardant resin composition which obtains flame retardancy from cyclic phosphonate added as a flame retardant to a blend of polypropylene resin and thermoplastic resin containing nitrogen atoms. However, it fails to disclose a flame retardant method for a polycarbonate resin and polycarbonate resin-based blend.